This invention relates generally to irrigation systems, and specifically to a device for distributing liquid uniformly over a desired area. More particularly, the invention provides a lawn sprinkler nozzle having no moving parts which distributes a plurality of bursts of discrete drops which oscillate in both horizontal and vertical planes.
The problems associated with the development of a low-cost, effective sprinkler or spray head, particularly for lawn or turf irrigation, have proven to be a technically fascinating but frustrating chore. Several different varieties are commercially available, and the literature is replete with many dozens of designs. In the past, systems have used such designs as a plurality of nozzles delivering a fixed irrigation pattern, mechanically rotated or oscillated nozzles delivering a generally narrow stream of water in an angular sweep, and various nozzle designs to provide generally dispersed jets of water. Most of these systems suffer from one or more shortcomings; for example, spray heads often produce a mist or fog rather than discrete droplets, thereby causing high evaporation losses and very poor distribution patterns particularly if a breeze exists, or, because of the fixed angle of stream exit, water is distributed non-uniformly over the area desired to be covered. Most small spray heads used in permanent lawn installations have narrow passageways which plug easily. Mechanically rotated units are cumbersome and expensive. Units having moving parts, such as are shown in Krynicki, U.S. Pat. No. 3,747,858, are subject to jamming or clogging from corrosion, traffic, dirt, or grass clippings.
Descriptions of several spray heads having pulsating or oscillating discharges formed without moving parts exist in the prior art. A nozzle having a flow-splitting "wedge" in a jet stream producing a very rapid oscillation in one plane is shown in Stauffer, U.S. Pat. No. 4,151,955. Frempter, U.S. Pat. No. 3,301,493 discloses a sprinkler head having an elongate cylindrical chamber and a single horizontal slotted discharge which produces a "fluttering" discharge apparently produced by interaction of water and air at the top of the cylindrical chamber. Hruby, U.S. Pat. No. 3,684,176 has a large chamber with an oblique inlet and a single long outlet duct at the top of the chamber to produce a pulsating spray. An oscillating spray is also produced in Hruby, U.S. Pat. No. 4,055,302 in a nozzle having a tortuous fluid path terminating in a single flared conical nozzle.
Non-oscillating sprinkler heads having a plurality of discharge apertures communicating with an interior chamber of vertically decreasing cross-section are shown in Svet, U.S. Pat. No. 2,311,266, and Garabedian, U.S. Pat. No. 2,493,719. The Svet patent shows a head having a plurality of bores in the hemi-ellipsoidal chamber wall. A large fastener extending vertically through the chamber, along with the ;arge discontinuity in the chamber wall at the bottom of the hemi-ellipsoid, and the large inlet channels at the sides of the chamber would all preclude this device from establishing a fluid-flow pattern necessary to produce oscillation. The Garabedian patent has an inverted conical head having a cap thereover; the cap is rotatable to permit holes in the cap to register with holes in the head to provide flow control. The Garabedian head, having a large inlet and ledge formed by the base of the conical cap and straight chamber side walls, again will not produce an oscillating spray.
It has been discovered in accord with the present invention that particular interior chamber geometries coupled with a critical ratio of chamber outlet to chamber inlet areas provides directionally unstable discharge of a series of discontinuous streams of discrete drops of varying velocities. Each stream of drops thus oscillates in both a vertical and horizontal plane. Stop-action photographs of the oscillating streams show that while the basic pattern of oscillation is random, control of vertical oscillatory frequency can be superimposed by proper alignment of the inlet relative to the output orifice array. Oscillation from each discharge orifice occurs through vertical angles of as much as 45.degree.-50.degree., and horizontal angles of up to about 20.degree., resulting in a very uniform distribution pattern. Sprinkler heads made in accord with the invention produce almost no misting even at high line pressures, thus reducing evaporation loss and imparting wind resistance to the liquid discharge of drops.
The oscillatory potential of the liquid discharge is a function of the design of the nozzle chamber. The chamber has a plurality of sharp-edged discharge ports in the chamber wall which extend to various extents (depending on whether full-, half-, quarter-head, or some other watering pattern is desired) around the periphery of the head. The chamber is entirely hollow and unobstructed, and has an upper wall portion which is curvilinear in both horizontal and vertical cross-sections. The upper chamber portion is preferably symmetrical about its vertical axis, having a circular or elliptic horizontal cross-section continuously decreasing in radius toward its uppermost portion (e.g., ellipsoidal, elliptic paraboloidal, or spherical). The lower portion of the chamber is curvilinear, preferably circular in horizontal cross-section, and may be straight or curvilinear in vertical cross-section. The width of the interior of the lower portion of the chamber either remains constant or decreases downwardly. An inlet port is located at the bottom of the chamber; for typical residential scale turf irrigation the area of the inlet port is importantly equal to or smaller than the total area of the outlet ports. The head functions as described herein because the jet of water exiting the inlet port interacts with the surrounding fluid and the chamber geometry to induce formation of a rapidly rotating, turbulent mass of water which travels along the chamber wall towards the discharge orifices. The aforesaid jet interaction with the ambient fluid and chamber geometry creates vortex-like cells of varying velocities within the main mass of rotating fluid. The differential velocities of the cells thus created cause the direction of the jet relative to the chamber walls to change periodically, thereby producing changes in direction of the turbulent rotating mass of fluid therein. Over a given time period the fluid mass thus approaches the discharge orifices from many different directions, thereby causing oscillations of the liquid discharge.
Accordingly, it is an object of the invention to provide liquid distribution apparatus which distributes discrete drops of liquid in a generally uniform distribution pattern. It is a further object of the invention to provide a sprinkler head which produces discontinuous streams of discrete drops which oscillate in multiple planes. It is yet a further object of the invention to provide a lawn sprinkler head having no moving parts, which is easily and inexpensively manufactured, and which provides relatively even ground coverage without production of aerosols. These and other objects of the invention will be evident from the following detailed description of preferred embodiments of the invention.